Inhalable contrast agent

ABSTRACT

A contrast agent is administered to a patient by inhalation into the patient&#39;s lungs. The agent is transmitted through the lungs into the patient&#39;s bloodstream, for transport to a non-lung portion of the patient to be imaged. A portion of the patient containing the microbubbles is subjected to an ultrasound scan, so as to obtain an enhanced ultrasonically generated image of the patient.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of imaging internal portionsof animal bodies.

2. Description of the Background Art

Images of internal structures and organs within a patient can beutilized for performing diagnosis and monitoring of patients. Suchinternal images can be obtained, for example, by ultrasonic imaging,magnetic resonance imaging (MRI) and optical imaging.

Ultrasonic images are formed utilizing reflected ultrasound waves, whichare detected and electronically converted into a visual display.

Ultrasonic imaging is particularly desirable when the internalstructures of interest within the patient can be imaged utilizing thereflected ultrasound alone. However, it sometimes is necessary toenhance the contrast of an ultrasound image by introducing a contrastagent into the patient. Heretofore, such ultrasound contrast agentstypically have been introduced into patients by injection.Unfortunately, injection of an ultrasound contrast agent into a patientdestroys the otherwise non-invasive advantage of ultrasonic imaging.

Other types of internal imaging, such as MRI and optical imaging, oftenalso require injection of contrast agents to enhance the images.

PCT International Publication No. WO 93/06869 to Vanderripe proposedinhalation of various gases to produce supersaturation in the blood forultrasound contrast.

Contrast enhanced magnetic resonance imaging of the airways of the lungshas been proposed using aerosolized gadopentetate dimeglumine inRadiology, 183: 667-672 (1992). However, there is no suggestion ofdelivery of contrast agent into the pulmonary circuit for MRIenhancement of non-lung tissue.

There remains a need in the art for methods and compositions forenhancing contrast during internal imaging of non-lung tissue inpatients, without the need for invasively injecting a contrast agentinto the patient.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method of imaging a non-lungportion of a mammal comprises administering an aerosol contrast agentcomprised of particles to a mammal by inhalation of the agent into alung of the mammal. The contrast agent is transmitted through the lunginto the mammal's bloodstream, and transported by the bloodstream to theportion of the mammal to be imaged. The mammal then is subjected to animaging scan, so as to obtain an enhanced image of the non-lung internalportion of the mammal.

The invention further encompasses an inhalable contrast agent whichcomprises an aerosol including particles which are capable of entering amammal's bloodstream through inhalation of the aerosol into a lung ofthe mammal. The particles form a contrast medium in the bloodstreamwhich is capable of enhancing images of the mammal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The contrast agents of the present invention do not require invasiveinjection of the agents into the body for internal image enhancement.Instead, the aerosol contrast agents of the present invention areadministered to a mammal by inhalation into a lung or lungs of themammal. The transport of such an agent is facilitated by the lung'slarge surface area (50 to 100 m²), thin membrane thickness (about 0.2m), high blood flow and rapid absorption characteristics.

Examples of inventive contrast agents include ultrasound contrastagents, MRI contrast agents and optical contrast agents. The inhaledcontrast agents of the invention also can provide therapeutic treatmentof the patient, if suitably configured.

An ultrasound contrast agent in accordance with one embodiment of thepresent invention comprises an aerosol including particles which arecapable of entering the mammal's bloodstream after inhalation of theaerosol into the mammal's lungs. The particles of the aerosol can be,for example, liquid or solid. The term "solid" as used herein, isintended to mean all particles which are not liquid, includingsemi-solid particles.

The aerosol can be produced in any well known means, e.g., by suspendingparticles in suitable propellants, such as fluorocarbon propellants,hydrocarbon propellants, ether propellants or compressed gases. Suchpropellants can also be utilized to form microbubbles in ultrasoundcontrast agents according to the present invention. Where liquidparticles are utilized, they can be saturated with one or more gaseouspropellants.

Suitable fluorocarbon and fluorohalocarbon propellants may includechlorotrifluoromethane (Freon 11), dichlorodifluoromethane (Freon 12),dichlorotetrafluoroethane, difluoroethane, hexafluoroethane,hexafluoropropane, pentafluoropropane, octafluoropropane,decafluorobutane, trichlorotrifluoroethane, trifluoroethane,monochlorodifluoroethane, monochlorodifluoromethane, trifluoropropaneand the like, including mixtures thereof.

Suitable hydrocarbon propellants in combination or individually mayinclude n-butane, isobutane, propane, methylbutane, pentane,cyclopropane and the like.

Suitable ether propellants may include dimethyl ether, ethyl ether,ethyl methyl ether, methyl t-butyl ether, and the like, and mixturesthereof.

Suitable compressed gases which may be used as propellants and to formmicrobubbles may include carbon dioxide, nitrous oxide, nitrogen,helium, neon, argon, krypton, xenon, etc.

Alternatively, the aerosol can be produced utilizing a suitable atomizeror nebulizer.

Particles of the aerosol according to the invention generally are lessthan about 25 microns in size. In preferred embodiments, particles aresmall enough to penetrate deep into the lungs so that they readily crossthe pulmonary alveolar membrane into the pulmonary bloodstream.Preferred particles are within a size range of about 0.1-10 microns insize, more preferably less than about 4 microns in size. In particularlypreferred embodiments, the aerosol is made up of particles within thesize range of about 0.1-3 microns so as to be transported into thealveolar sacs of the lungs.

According to one aspect of the invention for ultrasound use, inhaledparticles are utilized as conveyors of gas precursors or microbubbleprogenitors. The inhalation of gas precursors or microbubble progenitorsis far more efficient on a concentration basis than inhalation of a gasper se, as proposed in the previously cited Vanderripe PCT application.

In preferred embodiments, particles of the present invention forultrasound use form microbubbles in the bloodstream of the mammal afterentering the bloodstream through the mammal's lungs. The microbubblesformed in the bloodstream of the mammal are capable of enhancing anultrasonically generated image of the mammal.

Suitable microbubbles must be sufficiently small so as not to causeembolism in the mammal in which they are formed.

Ultrasound image-enhancing microbubbles generally are less than about 15microns in size, and preferably are predominantly about 8 microns insize or less. Microbubbles which are greater in size than about 8microns generally are too large to pass through the capillary beds ofthe lungs. A discussion of the effect of microbubble size in injectableultrasound contrast agents can be found in PCT International PublicationNo. WO 93/05819 to Steven C. Quay, claiming priority from U.S. Ser. Nos.07/761,311 (filed Sep. 17, 1991) and 07/893,657 (filed Jun. 5, 1992),incorporated herein by reference.

In particularly preferred embodiments of the present invention, themicrobubbles formed in the mammal's bloodstream are predominantly withinthe size range of about 0.5-8 microns, most preferably within the sizerange of about 1-7 microns.

In accordance with one aspect of the invention, the particles releaseultrasound contrast-enhancing microbubbles upon entering the bloodstreamof the mammal after inhalation. A particle comprised primarily of dilute(e.g., about 0.1-3% by weight) hydrogen peroxide (H₂ O₂), or hydrogenperoxide progenitor, is an example. When given intravenously, Wang, etal. in Chin. Med. J. 1979; 92, 595-599; and in Chin. Med. J. 1979; 92,693-702 and later Gaffney, et al. in Am. J. Cardiol. 1983, 52, 607-609demonstrated the use of dilute hydrogen peroxide (0.1-3%, 0.5 to 2.0 mL)to produce oxygen gas microbubbles on contact with the oxidases andperoxidases of the blood to produce dense opacification of the rightheart chamber with no complications. Particles of dilute hydrogenperoxide transported through the lungs into the pulmonary circulationlikewise present ultrasonic opacification.

The hydrogen peroxide can also be provided as an adjunct to radiotherapyfor treatment of neoplasms of the mammal.

In one preferred embodiment, the aerosol particles are liquid and themicrobubbles formed in the bloodstream are comprised of a gas. Suitablemicrobubble gases for use in accordance with the present invention aredisclosed in the previously cited PCT International Publication No. WO93/05819, and include fluorocarbons such as decafluorobutane andperfluoropentane. Organic liquids which may be suitable for use in thepresent invention are described in PCT International Publication No. WO89/06978 and European Patent Application No. 0 441 468 A2.

In particularly preferred embodiments, the liquid is substantiallybubble-free at room temperature (e.g., about 20° C.), and the liquidparticles form microbubbles when the temperature of the liquid is raisedto body temperature of the mammal, for example, about 37° C., uponinhalation of the liquid particles by the mammal. This embodimentutilizes a liquid-gas phase change wherein the liquid aerosol particlesremain a liquid or gas saturated liquid solution that cross thepulmonary alveolar membrane into the puliminary bloodstream, andthereafter release a sufficient volume of microbubbles due to anincrease in temperature of the liquid particles to body temperature uponentering the bloodstream.

Alternatively, liquid aerosol particles can produce microbubbles uponentering a mammal's bloodstream by chemically reacting with componentsof the bloodstream.

In preferred embodiments in which the aerosol particles are liquid, theliquid can be a viscous solution, for example, by inclusion of one ormore viscosity enhancers such as sorbitol. The use of viscous liquidscan reduce the rate at which the microbubbles dissolve into thebloodstream and dissipate. Liquid particles of the aerosol can furtherinclude one or more of the following types of components: isotonicelectrolytes such as NaCl, hydrophobic carrier liquids such as soybeanoil, surfactants such as Tween 20, water and permeation enhancers suchas dimethyl sulfoxide (DMSO) or 1-dodecylcylazacycloheptan-2-one (Azone)and/or ethanol.

In alternative embodiments, the particles of the aerosol are solid. Suchsolid particles can contain microbubbles and thus themselves comprisethe ultrasonic image-enhancing microbubbles which form in the mammal'sbloodstream. Alternatively, the solid particles can produce microbubblesupon entering the bloodstream by chemically reacting with components ofthe bloodstream. For example, a solid containing hydrogen peroxidewithin its structure such as inorganic phosphates, carbonates, and thelike, or organic compounds such as urea, and the like, can be used.

In embodiments in which the contrast agent forms ultrasoundimage-enhancing microbubbles in the bloodstream, an imaging scan isperformed by subjecting at least a portion of the mammal containing themicrobubbles to an ultrasound scan, so as to obtain an enhancedultrasonically generated image of that portion of the mammal.

In accordance with certain aspects of the present invention, aerosols ofMRI contrast agents, such as suitable metal chelates, are provided. Themetal chelates of the aerosol may include metals selected from the groupconsisting of lanthanide series members of atomic number 57-70, andtransition metal members having an atomic number selected from the groupconsisting of 21-29, 42 and 44.

Generally, such MRI contrast agents will further include apharmaceutically acceptable carrier.

Examples of paramagnetic metal chelate MRI contrast agents include Gd(DTPA)²⁻ :gadolinium (III)-diethylenetriamine-N,N,N',N",N"-pentaacetate;Gd(DTPA)-BMA:gadolinium(III)-diethylenetriamine-N,N,N',N",N"-pentaacetate-bis(methylamide);Dy(DTPA)²⁻:Dysprosium(III)-diethylenetriamine-N,N,N',N",N"-pentaacetate; GD(DOTA)⁻:gadolinium(III)-1,4,7,10-tetraazacyclododecane-N,N',N",N"-tetraacetate;Mn(CDTA)²⁻ :manganese(II)-trans--1,2-cyclohexylenedinitrilotetraacetate; Mn(NOTA)⁻:manganese(II)-1,4,7-triazacyclonoane-N,N',N"-triacetate; MN(EDTA)²⁻:manganese(II)-ethylenediaminetetracetate; Mn(HEDTA)⁻:managnese(II)-hydroxylethylethylenediaminetriacetate;Fe(EHPG):Iron(III)-N,N'-ethylenebis(2-hydroxyphenylglycine)ethylenediamine;FE(HBED):Iron(III)-N,N'-bis(2-hyroxybenzyl)ethylenediaminediacetate, andthe like.

Preferred MRI agents are chelates of Gadolinium, Iron or Manganese.

Suitable MRI agents may also include nitroxide radicals, otherstabilized radicals or oxygen gas. Stable organic free radicals includeDOXYL:(4,4-dimethyl-3-oxazolidinyloxy, free radical);PROXYL:(2,2,5,5-tetramethylpyrrolidine-1-oxyl, free radical, as anexample 2,2,5,5-tetramethylpyrrolidine-1-oxyl-3-carboxylic acid);TEMPO:(2,2,6,6-tetramethyl-1-piperidinyloxy, free radical, as an example2,2,6,6-tetramethyl-1-piperidine-1-oxyl-4-carboxylic acid), and thelike.

The particles of the aerosol can also comprise a solution or asuspension of highly fluorinated hydrocarbons for magnetic resonanceimaging of F¹⁹ nuclei. Such F¹⁹ MRI contrast agents can includebiocompatible formulations of perfluorocarbons, such asperfluorooctylbromide and the like.

Particles containing MRI contrast agent can further include a lungtissue permeation enhancing substance such as DMSO, Azone and/orethanol. Such permeation enhancing substances facilitate delivery ofsufficient concentrations of contrast agent into the pulmonary blood forenhanced imaging of organs such as the liver, spleen, heart, etc.

When the contrast agent of the invention is an optical contrast agent,it can provide either positive or negative optical contrast. An imagescan is performed by subjecting at least a portion of said mammalcontaining said agent to an optical scan utilizing electromagneticradiation, so as to obtain an enhanced optical image of said portion ofsaid mammal. Optical contrast agents according to the invention maycomprise suitable optical dyes, such as emr-absorbing andvoltage-sensitive dyes which are safe for in vivo administration. Suchdyes may be selected from the group consisting of cyanines,merocyanines, oxonols, styryl dyes, and the like. One such dye ismerocyanine oxazolone. The particles may comprise a solution or asuspension of the optical contrast agent, and may further comprise apermeation enhancing substance, such as dimethyl sulfoxide,1-dodecylcylazacycloheptan-2-one (Azone) and/or ethanol.

The invention is illustrated by the following examples, which are notintended to be limiting.

EXAMPLE 1

Chlorotrifluoromethane (Freon-11) was dissolved in dimethyl sulfoxide(DMSO) with Tween 20 surfactant. The solution thus formed remained astable, clear liquid at room temperature in a capped vial. The solutionproduced a visible blush of very small bubbles when poured into eitherdeionized 37° C. water or room temperature saline. This DMSO solutionexhibited greater density than either the water or saline, and quicklydropped to the bottom of the vial containing the mixture. Even severalminutes after combining with either the 37° C. water of the saline,subsequent mild agitation produced additional visible production of gasbubbles.

EXAMPLE 2

An ultrasound contrast agent as described in Example 1 is formed into anaerosol and inhaled by a patient so as to transmit the agent through thelungs of the patient into the patient's bloodstream, wherein the agentforms ultrasound image-enhancing microbubbles in the bloodstream. Thepatient then is subjected to an ultrasound scan, so as to obtain anenhanced ultrasonically generated image of the patient, primarily of theheart.

EXAMPLE 3

A 3% hydrogen peroxide solution was aspirated by a fluorocarbonpropellant sprayer into an intestinal membrane. The membrane was placedin a normal saline solution at 37° C. containing about 1% heparinizedcanine blood. Microbubbles were noted forming on the outer surface ofthe membrane within less than a minute. Application of an aerosol ofdeionized water produced no discernible microbubbles.

EXAMPLE 4

An aerosol of 0.2% hydrogen peroxide as outlined in Example 3 is inhaledby a patient so as to transmit the agent through the lungs of thepatient into the patient's bloodstream, wherein the agent formsultrasound image-enhancing oxygen microbubbles in the bloodstream. Thepatient then is subjected to an ultrasound scan, so as to obtain anenhanced ultrasonically generated image of the patient, primarily of theheart.

EXAMPLE 5

An aerosol of N,N"-bis(N-(2-methoxyethyl)carbamoylmethyl)diethylenetriamine-N,N',N'-triacetatogadolinium(III) in dimethylsulfoxide and water is inhaled by a patient so as to transmit the agentthrough the lungs of the patient into the patient's bloodstream, whereinthe contrast enhancing agent is delivered into the bloodstream. Thepatient then is subjected to an magnetic resonance scan, so as to obtainan enhanced image of the particular area of interest of the patient.

EXAMPLE 6

An aerosol containing merocyanine oxazolone is inhaled by a patient soas to transmit the agent through the lungs of the patient into thepatient's bloodstream, wherein the contrast enhancing agent is deliveredinto the bloodstream. The patient then is subjected to an optical scan,so as to obtain an enhanced image of the particular area of interest ofthe patient.

What is claimed is:
 1. A method of imaging a non-lung portion of mammal;comprising:a) administering an aerosol contrast agent comprised ofparticles to a mammal by inhalation of said agent into a lung of saidmammal, which agent is transmitted through said lung into the mammal'sbloodstream for transport to a non-lung portion of said mammal to beimaged; and b) performing an imaging scan on a non-lung portion of saidmammal containing said contrast agent, so as to obtain an enhanced imageof said non-lung internal portion of said mammal.
 2. The method of claim1 wherein said particles are selected from the group consisting ofliquid particles and solid particles.
 3. The method of claim 2 whereinsaid agent forms ultrasound image-enhancing microbubbles in saidbloodstream, and wherein said imaging scan is performed by subjecting atleast a portion of said mammal containing said microbubbles to anultrasound scan, so as to obtain an enhanced ultrasonically generatedimage of said portion of said mammal.
 4. The method of claim 3 whereinsaid agent further comprises a permeation enhancing substance.
 5. Themethod of claim 4 wherein said permeation enhancing substance isselected from the group consisting of dimethyl sulfoxide,1-dodecylcylazacycloheptan-2-one (Azone) and ethanol.
 6. The method ofclaim 3 wherein said particles release microbubbles upon entering saidbloodstream.
 7. The method of claim 6 wherein said particles of saidaerosol are liquid.
 8. The method of claim 7 wherein said microbubblescomprise at least one member selected from the group consisting ofhydrocarbons, fluorocarbons, fluorohalocarbons, ethers and mixturesthereof.
 9. The method of claim 7 in which said liquid is substantiallybubble-free at a temperature of about 20° C., wherein said liquid formsmicrobubbles when the temperature of said liquid is raised to about 37°C.
 10. The method of claim 9 wherein said microbubbles comprise at leastone member selected from the group consisting of fluorocarbon gases,fluorohalocarbon gases, hydrocarbon gases, volatile ethers and mixturesthereof.
 11. The method of claim 6 wherein said particles of saidaerosol are liquid containing at least one gas.
 12. The method of claim11 wherein said microbubbles comprise at least one gaseous propellant.13. The method of claim 2 wherein said agent is a magnetic resonancecontrast agent, wherein said agent provides either positive or negativeimage contrast, and wherein said image scan is performed by subjectingat least a portion of said mammal containing said agent to a magneticresonance scan, so as to obtain an enhanced magnetic resonance image ofsaid portion of said mammal.
 14. The method of claim 13 wherein saidparticles of said aerosol comprise metal chelates.
 15. The method ofclaim 14 wherein said metal chelates of said aerosol are selected fromthe group consisting of lanthanide series members of atomic numbers57-70, and transition metal members having an atomic number selectedfrom the group consisting of 21-29, 42 and 44; said agent furthercomprising a pharmaceutically acceptable carrier.
 16. The method ofclaim 14 wherein said metal chelates of said particles are selected fromthe group consisting of gadolinium chelates, iron chelates, andmanganese chelates.
 17. The method of claim 13 wherein said particles insaid aerosol comprise nitroxide radicals.
 18. The method of claim 17wherein said particles comprise a solution or a suspension of saidhighly fluorinated hydrocarbons said particles further comprising apermeation enhancing substance.
 19. The method of claim 18 wherein saidpermeation enhancing substance is selected from the group consisting ofdimethyl sulfoxide, 1-dodecytcylazacycloheptan-2-one (Azone) andethanol.
 20. The method of claim 13 wherein said particles of saidaerosol comprise highly fluorinated hydrocarbons for magnetic resonanceimaging of F¹⁹ nuclei.
 21. The method of claim 2 wherein said agentcomprises an optical contrast agent, wherein said optical contrast agentprovides either positive or negative optical contrast, and wherein saidimage scan is performed by subjecting at least a portion of said mammalcontaining said agent to an optical scan, so as to obtain an enhancedoptical image of said portion of said mammal.
 22. The method of claim 21wherein said agent is an optical dye.
 23. The method of claim 21 whereinsaid particles comprise a solution or a suspension of said opticalcontrast agent, said particles further comprising a permeation enhancingsubstance.
 24. The method of claim 23 wherein said permeation enhancingsubstance is selected from the group consisting of dimethyl sulfoxide,1-dodecylcylazacycloheptan-2-one (Azone) and ethanol.
 25. A contrastagent for imaging a non-lung portion of a mammal, which comprises anaerosol including particles which are capable of entering a mammal'sbloodstream through inhalation of said aerosol into a lung of themammal, wherein said particles, upon introduction into the bloodstreamof said mammal after inhalation by said mammal, form a contrast mediumin said bloodstream, which contrast medium is transported to a non-lungportion of said mammal and is capable of enhancing images of saidnon-lung portion of said mammal.
 26. The contrast agent of claim 25wherein said particles are selected from the group consisting of liquidand solid particles.
 27. The contrast agent of claim 26 wherein saidparticles form a contrast medium comprising microbubbles uponintroduction into said bloodstream, which microbubbles are capable ofenhancing an ultrasonically generated image of said non-lung portion ofsaid mammal.
 28. The contrast agent of claim 27 wherein said particlesof said aerosol are solid, and wherein said particles comprise saidmicrobubbles upon introduction into said bloodstream.
 29. The contrastagent of claim 27 wherein said particles release microbubbles uponentering said bloodstream.
 30. The contrast agent of claim 27 whereinsaid particles of said aerosol are liquid.
 31. The contrast agent ofclaim 30 wherein said microbubbles comprise at least one gaseouspropellant.
 32. The contrast agent of claim 30 in which said liquid issubstantially bubble-free at a temperature of about 20° C., wherein saidliquid forms microbubbles when the temperature of said liquid is raisedto about 37° C.
 33. The ultrasound contrast agent of claim 30 whereinsaid microbubbles comprise at least one member selected from the groupconsisting of fluorocarbon gases, fluorohalocarbon gases, hydrocarbongases, volatile ethers and mixtures thereof.
 34. The contrast agent ofclaim 30 wherein said particles further comprise at least one memberselected from the group consisting of hydrocarbons, fluorocarbons, andfluorohalocarbons.
 35. The contrast agent of claim 30 wherein saidparticles further comprise at least one propellant gas.
 36. The contrastagent of claim 30 wherein said particles are saturated with carbondioxide.
 37. The contrast agent of claim 25 wherein said particlesfurther comprise a permeation enhancing substance.
 38. The contrastagent of claim 37 wherein said permeation enhancing substance isselected from the group consisting of dimethyl sulfoxide,1-dodecylcylazacycloheptan-2-one (Azone) and ethanol.